Many types of metal articles or components, such as engine blocks, heads, oil and water pumps, brake cylinders, carburetors, transmission cases, etc., are manufactured by casting various metals or alloys, e.g. cast iron, aluminum, brass, magnesium, bronze, etc. Metal articles also are made by powdered metal techniques, in which metal powder is pressed in suitably shaped molds and then sintered at an elevated temperature to consolidate the structure, reduce porosity and impart useful strength; since this is essentially a solid diffusion process, a very high degree of dimensional accuracy is possible and large numbers of parts can be economically produced. A few examples of powdered metal articles are hydraulic pump components, gears, cams, bearings, injector bodies, levers and automotive trim.
With any of the metal casting and powdered metal processes in general use, it is typical for a varying proportion of cast articles and all powdered metal articles to have pores that extend through or partially through a wall of the articles. Because these pores can impair the usefulness of the article, such as by resulting in gaseous or fluid leakage, or preventing normal plating operations, the art of impregnating metal articles to fill the pores has developed in order that the articles can be made useful for their intended purpose.
The most effective technology for impregnation of metal articles is the "dry vacuum-pressure" method in which metal articles are placed in a closed vessel and the vessel is subjected to a vacuum (such as 2 to 10 Torr for 10 to 15 minutes) to cause air entrapped in any pores in the dry articles to escape. Liquid sealant is drawn from a reservoir into the vessel so as to cover and fill the pores of the article. The vacuum is then released and pressure is applied to the liquid sealant level (such as air at 100 psi for 10 to 15 minutes) to drive the sealant further into the pores. Following this, the excess sealant is drained, the parts rinsed with water to remove any remaining sealant, and the sealant in the pores is polymerized, i.e. cured, to fill the pores with solid material.
Another impregnation method is a "dry vacuum" process in which metal articles are placed in a closed vessel and the vessel is subjected to a vacuum (e.g. 2 to 10 Torr for 10 to 15 minutes) to cause air entrapped in any pores in the articles to escape. The articles are then submerged in or flooded by liquid sealant, so as to cover the articles and fill the pores and allowed to "soak" for 10 to 15 minutes at atmospheric pressure, following which excess sealant is drained, the articles are rinsed with water to remove any remaining sealant, and the sealant in the pores is polymerized to fill the pores with solid material.
Another commonly practiced technology for impregnation of metal articles is the so-called "wet vacuum" process that includes the steps of submerging the articles in a bath of liquid sealant in an enclosed impregnation tank, and then evacuating the tank to a sufficiently low vacuum (e.g. 2 to 10 Torr for 10 to 15 minutes) to enable most of the air entrapped in pores in the articles to escape so that the pores can be filled with liquid sealant. The vacuum in the impregnating tank is then released and the articles are transferred to a tank in which the excess sealant is allowed to drain off. The articles are transferred to another tank in which they are rinsed with water in order to wash off excess sealant. Next, the articles are transferred to a curing tank to allow the sealant to polymerize or cure to a solid material to fill the pores.
The sealants of choice for almost all cast metal articles and many powdered metal articles are liquid, water-soluble, heat curable sealants containing methacrylate or methacrylate/polyester resins that polymerize in the presence of air or oxygen.
These sealants are of interest to end users since they can be cured at relatively low temperatures in relatively short time periods, such as by curing with hot water in a temperature range of about 85.degree. C. to 90.degree. C. for a period of about 4 minutes to 15 minutes. Rapid curing at moderate temperatures facilitates impregnation of metal articles and reduces the time required for processing the articles.
Since the first acceptance in industry some 40 years ago of water soluble sealants, the post impregnation rinse waters, which are generated in the practice of all of the above-described methods and which are usually contaminated with methacrylates, polyesters, dyes, catalysts and surfactants to a greater or lesser degree, have been routinely flushed into metropolitan sewage systems. However, today although the methacrylate and polyester resins are not hazardous they cannot be disposed of in most metropolitan sewage systems because they test out as "grease" and "oil" when tested in accordance with EPA standards. Therefore, their presence is being monitored and any violations of the EPA standards are being enforced with ever-increasing stringency.
Various methods of removing the resins from the rinse water have been attempted. In one method, the rinse water is simply boiled, to polymerize the resin present (thus changing the resin state from liquid to solid and rendering it useless) and then filtering out the resulting solid. This method is expensive and requires disposal of the collected solids which might be considered in some situations to be "hazardous substances".
Another method employs the addition of high molecular, non-ionic surfactants which have hydrocarbon mitigating properties. This method also is very expensive and once the surfactant/resin emulsion is removed from the water, it is almost impossible to separate the surfactant from the resin. The result is that neither can be reused.
It would be advantageous to have a simple, inexpensive method of removing resin from the rinse water which permits the resin to be recovered and reused.